Separation of -ketals



EEPARATIGN F KETALS George Claude Bond, Freeport, and Lloyd Albert Klar, Lake Jackson, Ten, assignors to The Dow Chemical Company, Midland, Mich, a corporation of Delaware No'DraWing. Application March 1, 1956 Serial No. 568,712

12 Claims. (Cl. 260-416) This invention relates to a process for separation of ketals from mixtures containing water, alcohol, ketone and ketal. More particularly, it relates to the separation of lower ketals from mixtures containing water, primary alcohols having from 1 to 3 carbon atoms, k etones having from 3 to 5 carbon atoms, and the lower ketals in concentrations greater than 5 percent by weight.

Recently, a method for preparation of ketals by a direct additive reaction of a ketone and an alcohol has been discovered. In this process the ketal produced is in a reaction product which contains some of the reactants, alcohol and ketone, and water, with the concentration of the ketal being, usually, from to weight percent. The reaction is reversible and a problem is encountered in attempting to separate the ketal from this mixture without hydrolyzing the product. In addition to the hydrolyzation, the physical properties of the components in the reaction product are such that the usual methods for separation of hydrocarbons are not efiective, especially when the concentrations of the ketal are below weight percent. In distillation of the mixture, close boiling point azeotropes are obtained rendering the separation impractical. The extraction of the ketal by organic solvents is likewise impractical due to the mutual solubilities of the constituents.

It is, therefore, the principal object of this invention to provide a method whereby ketals can be separated easily from mixtures containing alcohol, ketone, water, and ketal without hydrolyzation of the product and to provide a method which would be applicable even when the concentration of ketal in such mixtures is relatively'small.

The process for separation of a lower ketal from a mixture containing water, primary alcohols having from 1 to 3 carbon atoms, ketones having from 3 to 5 carbon atoms, and the lower ketals in amounts greater than 5 weight percent according to the invention, comprises contacting the above mixture with an aqueous solution containing from 10 to weight percent of a strong hydroxide, such as sodium hydroxide and potassium hydroxide, in amounts such that the volume ratio of the hydroxide solution to the ketal solution is in the range of /2 to 20 to extract the major part of the other constituents from the ketal, and recovering the ketal.

The term lower ketal as used herein means the ketals represented by the general formula:

1 to 3 carbon atoms, and R and R represent alkyl groups having from 1 to 2 carbon atoms.

2,8214%" Patented Mar. 18, 1958 ice In the process the mixture of alcohols, 'ketones, water, and ketal, can be contacted with the strong hydroxide solutions in batch or continuous operation. No special equipment is required, and the known types of extraction equipment operated according-to the'accepted engineering practice may be used. When a batch operation is used, it is preferred to divide the hydroxidesolution in several parts and to use a simple multistage contact extraction, the procedure being to add part of the hydroxide to the ketal mixture, separate the'ketal-containing part from the resulting heterogeneous solution, and to again contact this recovered ketal-containing portion with more fresh hydroxide. A continuous countercurrent process is more convenient. The equipment can be selected and operated under the known engineering practices so that, preferably, more than one theoretical contact stage is obtained. When a single contact stage is used, the ketal-containing portion of the heterogeneous mixture will be about percent ketal and contain about percent of the total ketal. When using more than one ideal contact stage, itis possible to recover practically all of the ketal from the mixture as a product containing 97 percent ketal and the remainder being acetone and Water. The necessary number of stages to obtain the above high yields are relatively few, usually less than 3. \V'nen more than 3 ideal stages are used, very little additional improvement in the recovery or purity of the product is obtained.

The concentration of the hydroxide used is critical. To obtain any recovery of the ketal the concentration of the hydroxide must be at least 10 weight percent. A very sharp improvement in ketal recovery is evidenced when the concentration of the hydroxide is increased from 10 to 16 percent. When the concentration of the solution is further increased, from 16 to 30, only a slight gradual improvement is obtained. Thus, it is preferred to use a hydroxide solution of 13 to 16 percent concentration.

The volume ratio of hydroxide solution to the ketal solution used may be varied over a wide range from /2 to 20. The amounts of hydroxide solution used will afiect both the recovery of the ketal and the concentration of the ketal in the ketal product. When small amounts of hydroxide are used, the recovery of the ketal is not complete and the product contains a low concentration of ketal. When the amounts are increased to over 20 times the ketal solution, the product will be practically pure ketal, but the recovery is low. The optimum ratio is to use the hydroxide in amounts about 2 to 5 times the volume of ketal solution.

The ratio of ketone to alcohol in the ketal mixture and the temperature do not materially afiect the recovery. For convenience, the separation is usually carried out at room temperature. Lower temperatures would favor the recovery, but the improvement is not suflicient to offset the additional cost of cooling.

By this process, practically all of the ketal can be easily recovered in a product having over percent ketal. If it is desirable to further purify the ketal, this may easily be done by vacuum distillation, or the product can be chemically dried and then distilled at atmospheric pressures. The lower ketals will hydrolyze in the presence of water at high temperatures so that it is necessary to eifect the distillation at a low temperature, or to remove the water. In the product as recovered after the hydroxide extraction, the amount of alcohol and ketone present with the ketal will not create azeotropic tone, and 5 percent Water.

problems upon distillation. .The alcohol andracetone'extracted by the hydroxide may be easily separated from the hydroxide solution by disillation and returned to the process.

The following examples will further illustrate the invention- In the examples, the percent as given is in weight percent. 7

Example] 80 gramsof ketal mixture containing 73.8 percent methanol, 9.8 percent acetone, 14.0 percent 2,2-dimethoxypropane and 2.4 percent water were placed in a separatory funnel. 525 grams of 15 percent sodium hydroxide solution were added to the ketal mixture. The layers of the resulting heterogeneous solution were separated and analyzed.

The ketal layer weighed 10.5 grams and contained 89 percent ketal, 8.6 percent acetone and methanol, and 2.4 percent water. The sodium, hydroxide layer weighed 594.5 grams and contained 0.3 percent ketal, 11.0 percent alcohol and acetone, and 88.7 percent caustic solution. This one stage contact gave an 83'percent recovery 1 of the ketal in a product containing 89' percent ketal.

. 7 Example II c 7 i The same procedure as in Example I was followed.

The ketal mixture used contained 52.2 grams of methanol, 10.1 grams of acetone, 2.7 grams of water, and 15.2 grams of 2,2-dimethoxypropaner To this mixture, 315 grams of 15 percent sodium hydroxide solution were 7 added.

The ketal layer obtained'weighed 163 grams and contained 84 percent ketal, 2 percent alcohol, 9 percent ace- The caustic layer weighed 348.9 grams and contained 13 percent sodium hydroxide, 71 percent water, 2 percent acetone, 14 percent alcohol and 0.4 percent ketal. .This gave a 90.1percent recovery of the ketal in'a ketal,

Example III The same procedure as in'Example I was followed.

The ketal mixture used contained 75.2 grams of ethanol, 9.3 grams of acetone, 3.1 grams H and 22.4 grams product containing 84 percent solution containing water, a primary alcohol having from 1 to 3 carbon atoms, a ketone having from 3 to 5 carbon atoms, and the ketal in an amount greater than 5 weight percent, which comprises contacting the solution 5 with an aqueous solution containing from to 30 weight percent of a strong hydroxide selected from the group consisting of sodium hydroxide and potassium hydroxide in an amountsuch that the volume ratio of the hydroxide solution to the ketal solution is in the range of to 0 to form a heterogeneous solution of a ketal-containing phase and a hydroxide phase, and separating the ketalcontaining phase from the hydroxide phase.

2. A process, according to claim 1 wherein the stron hydroxide is sodiumhydroxide.

3. A process according to claim'l wherein the strong hydroxide is potassium hydroxide. V

4. A process for separation of a lower ketal from a solution containing water, a' primary alcohol having from 1 to 3 carbon atoms, a ketone having from 3 to 5 20 carbon atoms, and the ketal in an amount greater than 5 weight percent and up to 97 weight percent, which comprises contacting the solution with an aqueous solution containing from 13 to 16 weight percent of sodium hydroxide in an amount such that the volume ratio of the 5 sodium hydroxide solution to the ketal solution is in the range of 2 to 5 to form a heterogeneous solution of a ketal-containing'phase and a hydroxide phase, and separating the ketalcontaining phase from the hydroxide phase. t

5. A process according to claim 4 wherein the lower ketal is 2,2-dimethoxypropane, the primary alcohol is methanol, and the ketone is acetone."

6. A'process for separation of a lower solution 'containing water, a primary alcohol having from 5 "1 to 3 carbon atoms, a ketone having from 3 to 5 carbon atoms, and the ketal in an amount greater than 5 weight percent andup to 97 weight percent which comprisescontacting the solution with an aqueous solution containing from'13 to 16 weightpercent of potassium hy- 40 droxide in an amount suchthat the volume ratio of the of 2,2-diethoxypropane. To this mixture, 432grams of 15 percent sodium hydroxide solution were added.

The ketal layer weighed 23.5 grams and was composed of 21.3 grams of diethoxypropane, 0.5 gram of ethanol,

1.0 gram of acetone and 0.7 gram'of water. The sodium hydroxide layer weighed 518.5 grams and contained 1.1

grams of diethoxypropane, 74.7 grams :of ethyl alcohol,

8.3 grams acetone, 369.4 hydroxide. V

This gave a 95 percent recovery of the ketal in a prodnot containing 90.5 percent ketal. T

Example IV A 35 foot column, 6 inches in diameter and-packed grams H 0 and 65 grams sodium to a depth of 30 feet with 2 inch steelrings, was operated V at atmospheric temperature and pressure. A ketal mixture containing 67.0 percent methanol, 19.6 percent acetone, 2.1' percentwater, and 11.3 percent 2,2-dimethoxypropane was fed to the bottom of the column at a rate of 271 pounds per hour and a 16.7 percent sodium hy- 1029 poundsperhour. 1 1 c 1 Ketal product was removed from thtop ofl thetower at a rate of 31.4 pounds perhou'rwhiclr contained 97 percent 2,2-dimethoxypropane, 1.5 percent acetone, 1.5

14. 3 precent methanol, 42 percentjaceton'e,68.1.percent 1 .1. A process for separation of a'lowerketal from a droxide solution was intrdduced at the top at a rate of 45 phase.

I'percent waten and a trace of methanol; ,Thelcaustic 'solution'obtained at the bottom of-the columnicontaine'd 7 g Water, and 13.6 percent sodium hydroxide. This gave a 99.67 percentrecovery of ketal as a 97...percentconcentrated product. I a r We claim:

a ketal-containing phase and a hydroxide phase, and

separating the ketal containing phase from the hydroxide 7. A process according to claim6 wherein the lower ketal is 2,2-dimethoxypropane,- the methanol, and the ketone is acetone.

8. A process for the separation of a lower ketal from a solution containing water, a primary alcohol having from 1 to 3 carbon atoms, a ketone having from 3 to 5 carbon atoms, and the ketal in an amountfrom 10 to 20 weight percent, which comprises contacting the solution with an aqueous solution containing from 10 to 30 weight percent of a strong hydroxide selected fromithe'group consisting of sodium hydroxide and potassium hydroxide in an amount such that the volume ratio of the hydroxide solution to the ketal solution is in the range of to 20 to form a heterogeneous solution of a ketal-containing phase and a hydroxide phase, and separating the ketal-containing phase from the hydroxide phase.

9. A process for the separation of a lower ketal from a'solution containing water, a primary alcohol having from 1 to' 3 carbon atoms, a ketone having from 3 to 5 5 carbon atoms, and the ketalin an amount from 10 to'20 weight percent, which comprises contacting the solu xtion with an aqueous solution containing from 13 to 16 Weight percent of sodium hydroxide in an amount such that the volume ratio of the sodium hydroxide solution to the ketal solution is in the range of 2 to 5 to form a heterogeneous solution of aketal-containing phase and a hydroxide phase, and separating the ketal-containing ketal from a primary alcohol is 11. A process for the separation of a lower ketal from a solution containing water, a primary alcohol having from 1 to 3 carbon atoms, a ketone having from 3 to 5 carbon atoms, and the ketal in an amount from 10 to 20 weight percent, which comprises contacting the solution with an aqueous solution containing from 13 to 16 weight percent of potassium hydroxide in an amount such that the volume ratio of the potassium hydroxide solution to the ketal solution is in the range of 2 to 5 to form a heterogeneous solution of a ketal-containing phase and 10 2,490,337

6 a hydroxide phase, and separating the ketal-containing phase from the hydroxide phase.

12. A process according to claim 11 wherein the lower ketal is 2,2-dimethoxypropane, the primary alcohol is 5 methanol, and the ketone is acetone.

References (Zited in the file of this patent UNITED STATES PATENTS Croxall et al. Dec. 6, 1949 

1. A PROCESS FOR SEPARATION OF A LOWER KETAL FROM A SOLUTION CONTAINING WATER, A PRIMARY ALCOHOL HAVING FROM 1 TO 3 CARBON ATOMS, A KETONE HAVING FROM 3 TO 5 CARBON ATOMS, AND THE KETAL IN AN AMOUNT GREATER THAN 5 WEIGHT PERCENT, WHICH COMPRISES CONTACTING THE SOLUTION WITH AN AQUEOUS SOLUTION CONTAINING FROM 10 TO 30 WEIGHT PERCENT OF A STRONG HYDROXIDE SELECTED FROM THE GROUP CONSISTING OF SODIUM HYDROXIDE AND POTASSIUM HYDROXIDE IN AN AMOUNT SUCH THAT THE VOLUME RATIO OF THE HYDROXIDE SOLUTION TO THE KETAL SOLUTION IS IN THE RANGE OF 1/2 TO 20 TO FORM A HETEROGENEOUS SOLUTION OF A KETAL-CONTAINING PHASE AND A HYDROXIDE PHASE, AND SEPARATING THE KETALCONTAINING PHASE FROM THE HYDROXIDE PHASE. 